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Ask Michael Warfield Your Own Question
Michael Warfield
Michael Warfield, Factory Mercedes-Benz Technician
Category: Mercedes
Satisfied Customers: 3130
Experience:  Mercedes-Benz Master Certified technician
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My Merc GL500 only has Park, Reverse and first gear. It will

Customer Question

My Merc GL500 only has Park, Reverse and first gear. It will not move up from first.
It has been a regular issue sticking in a high gear. Usually fixed by turning off engine and restarting. This does not work currently and I only have 1st gear and won't change up.
This also happened 4 weeks ago. Merc. service said the transmission had lost its program and they reset for me.
I have had constant issues with this and other electricals (you helped out with the Command System in 2011)
I am hoping there is a fuse/fuses I can remove and re-seat that will reset the transmission so that I can drive to a service agent or to get me out of trouble if this happens more regularly
Thanks
Tony
Submitted: 1 year ago.
Category: Mercedes
Expert:  Michael Warfield replied 1 year ago.

What actually happens with this transmission is a failure of the turbine speed sensor located on the electrics plate of the valve body. It causes this "limp" mode as a sort of self protection. It is a very common problem on the early suv models unfortunately. I would recommend getting the fault codes scanned of the transmission computer and if there is indeed a turbine speed sensor fault, the whole electrics plate will have to be ordered from a dealership and programmed. The cost of this unfortunately, is about $1000-1200.

Customer: replied 1 year ago.
I have had messages on dash before saying "do not change gear drive to a service centre" but nothing indicating limp or safe mode go to service centre this time. There are no fault messages at all this time. The fact that it worked after a reset of transmission values (that were lost due to unknown electrical issue makes me hope there is something I can do by removing and re-seating fuses or to disconnect the battery perhaps? I am too far away from a service centre to drive at 15-20mph max speed.
I really am hoping for a brief fix in order to get the vehicle to service centre
Any other thoughts please?
Thanks
Tony
Expert:  Michael Warfield replied 1 year ago.

When the vehicle goes into limp mode, it doesn't tell you. It also may not give you a check engine light. When you say there are no fault codes, what type of scanner are you using? If it is a basic OBD scanner, it will only be able to read the engine fault codes and not of the ETC or ISM modules necessary to diagnose the problem. Its pretty unusual for the transmission to be stuck in a gear and not have any faults stored in the transmission or ISM modules. If you are getting the do not change gears and drive to workshop message, it can be faulty software in the ISM shift module. I would rather have new software tried in the ISM module before I replace it (expensive). Have you tried disconnecting the ground cable on the battery under the passenger front seat to see if it will reset?

Customer: replied 1 year ago.
Tried with no success
Thanks anyway
Expert:  Michael Warfield replied 1 year ago.

Sorry, but good luck. It looks like a tow is unavoidable at this point. The conductor plate or ISM has failed beyond a simple reset.